1. Field of the Invention
The present invention relates to a recording medium for ink-jet recording and more particularly to a recording medium of excellent ink absorptiveness and clearness of the image recorded thereupon.
2. Description of the Prior Art
The ink-jet recording process involves ejecting small droplets of recording liquid (ink) by various ink-discharging techniques (e.g., the technique utilizing electrostatic attraction, technique of vibrating or displacing ink mechanically by use of piezo elements, technique utilizing the foaming pressure of ink generated by heating) and depositing parts or all of the ejected droplets onto a recording medium such as paper, thereby performing the recording.
Ink-jet recording is noticed as a recording method which generates limited noises and permits a high-speed recording and multicolor printing. For the ink-jet recording, recording liquids containing water as the main component are predominantly used for reasons of safety and recording characteristics, and in many cases a polyhydric alcohol is added thereto so as to prevent the clogging of the nozzles and improve the discharge stability.
Recording media hitherto used for the ink-jet recording are usual plain paper and so-called ink-jet recording paper that comprises a substrate and a porous, ink absorbing layer laid thereupon. However, more sophisticated and comprehensive performance characteristics are increasingly required of the recording media, with improvements in the performance of ink-jet recording apparatuses, such as the speed-up of recording and the development of multicolor recording, and with expanding use of ink-jet recording apparatuses. That is to say, the recording medium for ink-jet recording needs to fulfill the following various fundamental requirements on performance characteristics in order to form high resolution, high quality images.
(1) The recording medium should absorb ink as quickly as possible.
(2) An ink dot, when overlapping a previously applied ink dot, should not disorder it.
(3) Ink droplets should not diffuse on the recording medium, or the diameters of ink dots should not be more enlarged than is necessary.
(4) The shapes of ink dots should be close to a right circle and the perimeters of ink dots should be smooth lines.
(5) Ink dots should have high OD (optical density) and distinct perimeter lines.
In addition to these characteristics, the following characteristics are required of the recording medium in order that images of high resolution comparable to that of color photographs may be obtained by the multi-color ink-jet recording process.
(6) Colorants in the inks applied onto the recording medium should show excellent color developing properties.
(7) The recording medium should be excellent particularly in its ability to fix inks since in some cases ink dots of the same number as that of the colors of inks employed are deposited onto the same spot to overlap one another.
(8) The recording medium should have a glossy surface.
(9) The recording medium should show a high brightness.
In the past, recording media for ink-jet recording were exclusively used for the purpose of obtaining non-light-transmitting type image: (surface image observation purpose). However, with improvements in the performance of ink-jet recording apparatuses and with expanding use thereof, demands are growing for recording media suited for purposes other than the surface image observation purpose. Such new applications of recording media include, for example, the projection of a recorded image onto a screen or the like by use of an optical device such as a slide or OHP (overhead projector), color separation plates for making positive plates used in color printing, and CMF's (color mosaic filters) for use in liquid crystal color display devices and the like.
Diffuse light scattered by recorded images is observed when the recording media are used for the surface image observation purpose. On the contrary, the light transmitted by the formed image is of main concern when the recording media are used for the above new purposes.
Accordingly, excellent transparency and particularly excellent linear transmittance are required besides the above noted requirements for ink-jet recording media. However, a recording medium of light-transmitting type has not yet been found that fulfills all the above noted requirements.
Most of the conventional recording media of non-light-transmitting type have a porous, ink absorbing layer at the surface to absorb the ink into the voids of the layer. Therefore, the surface of such recording media is non-glossy because of the porous state. On the other hand, when the ink-absorbing surface layer is non-porous, nonvolatile components such as a polyhydric alcohol contained in the applied ink will remain for a long time on the surface; that is, a long time is required for drying or fixing the ink; in consequence, such recording media are disadvantageous in that the formed image, on contacting with an object, e.g., clothing, will stain it or be impaired.